Latest research in football - week 50 - 2013

As previous literature updates, we have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Soccer activity profile of altitude versus sea-level natives during acclimatisation to 3600 m (ISA3600)Authors: Aughey RJ, Hammond K, Varley MC, Schmidt WF, Bourdon PC, Buchheit M, Simpson B, Garvican-Lewis LA, Kley M, Soria R, Sargent C, Roach GD, Claros JC, Wachsmuth N, Gore
CJ.Reference: Br J Sports Med. 2013 Dec;47 Suppl 1:i107-i113. doi: 10.1136/bjsports-2013-092776.Download Link:http://bjsm.bmj.com/content/47/Suppl_1/i107.full.pdf+htmlSummary: We investigated the effect of high altitude on the match activity profile of elite youth high altitude and sea level residents. Twenty Sea Level (Australian) and 19
Altitude-resident (Bolivian) soccer players played five games, two near sea level (430 m) and three in La Paz (3600 m). Match activity profile was quantified via global positioning system with
the peak 5 min period for distance ((D5peak)) and high velocity running (>4.17 m/s, HIVR5peak); as well as the 5 min period immediately subsequent to the peak for both distance (D5sub) and
high-velocity running (HIVR5sub) identified using a rolling 5 min epoch. The games at 3600 m were compared with the average of the two near sea-level games. The total distance per minute was
reduced by a small magnitude in the first match at altitude in both teams, without any change in low-velocity running. There were variable changes in HiVR, D5peak and HiVR5peak from match to
match for each team. There were within-team reductions in D5peak in each game at altitude compared with those at near sea level, and this reduction was greater by a small magnitude in Australians
than Bolivians in game 4. The effect of altitude on HiVR5peak was moderately lower in Australians compared with Bolivians in game 3. There was no clear difference in the effect of altitude on
maximal accelerations between teams. High altitude reduces the distance covered by elite youth soccer players during matches. Neither 13 days of acclimatisation nor lifelong residence at high
altitude protects against detrimental effects of altitude on match activity profile.

#2 Wellness, fatigue and physical performance acclimatisation to a 2-week soccer camp at 3600 m (ISA3600)Authors: Buchheit M, Simpson BM, Garvican-Lewis LA, Hammond K, Kley M, Schmidt WF, Aughey RJ, Soria R, Sargent C, Roach GD, Claros JC, Wachsmuth N, Gore CJ, Bourdon PC.Reference: Br J Sports Med. 2013 Dec;47 Suppl 1:i100-i106. doi: 10.1136/bjsports-2013-092749.Download Link:http://bjsm.bmj.com/content/47/Suppl_1/i100.full.pdf+htmlSummary: To examine the time course of wellness, fatigue and performance during an altitude training camp (La Paz, 3600 m) in two groups of either sea-level (Australian) or
altitude (Bolivian) native young soccer players. Wellness and fatigue were assessed using questionnaires and resting heart rate (HR) and HR variability. Physical performance was assessed using HR
responses to a submaximal run, a Yo-Yo Intermittent recovery test level 1 (Yo-YoIR1) and a 20 m sprint. Most measures were performed daily, with the exception of Yo-YoIR1 and 20 m sprints, which
were performed near sea level and on days 3 and 10 at altitude. Compared with near sea level, Australians had moderate-to-large impairments in wellness and Yo-YoIR1 relative to the Bolivians on
arrival at altitude. The acclimatisation of most measures to altitude was substantially slower in Australians than Bolivians, with only Bolivians reaching near sea-level baseline high-intensity
running by the end of the camp. Both teams had moderately impaired 20 m sprinting at the end of the camp. Exercise HR had large associations (r>0.5-0.7) with changes in Yo-YoIR1 in both
groups. Despite partial physiological and perceptual acclimatisation, 2 weeks is insufficient for restoration of physical performance in young sea-level native soccer players. Because of the
possible decrement in 20 m sprint time, a greater emphasis on speed training may be required during and after altitude training. The specific time course of restoration for each variable suggests
that they measure different aspects of acclimatisation to 3600 m; they should therefore be used in combination to assess adaptation to altitude.

#3 Predicting sickness during a 2-week soccer camp at 3600 m (ISA3600)Authors: Buchheit M, Simpson BM, Schmidt WF, Aughey RJ, Soria R, Hunt RA, Garvican-Lewis LA, Pyne DB, Gore CJ, Bourdon PC.Reference: Br J Sports Med. 2013 Dec;47 Suppl 1:i124-i127. doi: 10.1136/bjsports-2013-092757.Download Link:http://bjsm.bmj.com/content/47/Suppl_1/i124.full.pdf+htmlSummary: To examine the time course of changes in wellness and health status markers before and after episodes of sickness in young soccer players during a high-altitude training
camp (La Paz, 3600 m). Wellness and fatigue were assessed daily on awakening using specifically-designed questionnaires and resting measures of heart rate and heart rate variability. The rating
of perceived exertion and heart rate responses to a submaximal run (9 km/h) were also collected during each training session. Players who missed the morning screening for at least two consecutive
days were considered as sick. Four players met the inclusion criteria. With the exception of submaximal exercise heart rate, which showed an almost certain and large increase before the day of
sickness (4%; 90% confidence interval 3 to 6), there was no clear change in any of the other psychometric or physiological variables. There was a very likely moderate increase (79%, 22 to 64) in
self-reported training load the day before the heart rate increase in sick players (4 of the 4 players, 100%). In contrast, training load was likely and slightly decreased (-24%, -78 to -11) in
players who also showed an increased heart rate but remained healthy. A >4% increased heart rate during submaximal exercise in response to a moderate increase in perceived training load the
previous day may be an indicator of sickness the next day. All other variables, that is, resting heart rate, heart rate variability and psychometric questionnaires may be less powerful at
predicting sickness.

#4 Methods of the international study on soccer at altitude 3600 m (ISA3600)Authors: Gore CJ, Aughey RJ, Bourdon PC, Garvican-Lewis LA, Soria R, Claros JC, Sargent C, Roach GD, Buchheit M, Simpson BM, Hammond K, Kley M, Wachsmuth N, Pepper M, Edwards A,
Cuenca D, Vidmar T, Spielvogel H, Schmidt WF.Reference: Br J Sports Med. 2013 Dec;47 Suppl 1:i80-i85. doi: 10.1136/bjsports-2013-092770.Download Link:http://bjsm.bmj.com/content/47/Suppl_1/i80.full.pdf+htmlSummary: We describe here the 3-year process underpinning a multinational collaboration to investigate soccer played at high altitude-La Paz, Bolivia (3600 m). There were two
main aims: first, to quantify the extent to which running performance would be altered at 3600 m compared with near sea level; and second, to characterise the time course of acclimatisation of
running performance and underlying physiology to training and playing at 3600 m. In addition, this project was able to measure the physiological changes and the effect on running performance of
altitude-adapted soccer players from 3600 m playing at low altitude. A U20 Bolivian team ('The Strongest' from La Paz, n=19) played a series of five games against a U17 team from sea level in
Australia (The Joeys, n=20). 2 games were played near sea level (Santa Cruz 430 m) over 5 days and then three games were played in La Paz over the next 12 days. Measures were (1) game and
training running performance-including global positioning system (GPS) data on distance travelled and velocity of movement; (2) blood-including haemoglobin mass, blood volume, blood gases and
acid-base status; (3) acclimatisation-including resting heart rate variability, perceived altitude sickness, as well as heart rate and perceived exertion responses to a submaximal running test;
and (4) sleep patterns.Pivotal to the success of the project were the strong professional networks of the collaborators, with most exceeding 10 years, the links of several of the researchers to
soccer federations, as well as the interest and support of the two head coaches.

#5 The impact of altitude on the sleep of young elite soccer players (ISA3600)Authors: Sargent C, Schmidt WF, Aughey RJ, Bourdon PC, Soria R, Claros JC, Garvican-Lewis LA, Buchheit M, Simpson BM, Hammond K, Kley M, Wachsmuth N, Gore CJ, Roach GD.Reference: Br J Sports Med. 2013 Dec;47 Suppl 1:i86-i92. doi: 10.1136/bjsports-2013-092829.Download Link:http://bjsm.bmj.com/content/47/Suppl_1/i86.full.pdf+htmlSummary: Altitude training is used by elite athletes to improve sports performance, but it may also disrupt sleep. The aim of this study was to examine the effects of 2 weeks at
high altitude on the sleep of young elite athletes. Participants (n=10) were members of the Australian under-17 soccer team on an 18-day (19-night) training camp in Bolivia, with six nights at
near sea level in Santa Cruz (430 m) and 13 nights at high altitude in La Paz (3600 m). Sleep was monitored using polysomnography during a baseline night at 430 m and three nights at 3600 m
(immediately after ascent, 1 week after ascent and 2 weeks after ascent). Data were analysed using effect size statistics. All results are reported as comparisons with baseline. Rapid eye
movement (REM) sleep was likely lower immediately upon ascent to altitude, possibly lower after 1 week and similar after 2 weeks. On all three nights at altitude, hypopneas and desaturations were
almost certainly higher; oxygen saturation was almost certainly lower; and central apnoeas, respiratory arousals and periodic breathing were very likely higher. The effects on REM sleep were
common to all but one participant, but the effects on breathing were specific to only half the participants. The immediate effects of terrestrial altitude of 3600 m are to reduce the amount of
REM sleep obtained by young elite athletes, and to cause 50% of them to have impaired breathing during sleep. REM sleep returns to normal after 2 weeks at altitude, but impaired breathing does
not improve.

#6 Relative Risk for Concussions in Young Female Soccer PlayersReference: Appl Neuropsychol Child. 2013 Dec 2. [Epub ahead of print]Authors: Strand S, Lechuga D, Zachariah T, Beaulieu K.Summary: The objective of this study was to determine the relative risk and reported symptoms of concussions in 11- to 13-year-old, female soccer players. For this, a survey to
compare the reported incidence of concussion in age-matched female soccer players to non soccer players was performed. The survey included 342 girls between the ages of 11 and 13: 195 were
involved in an organized soccer team and 147 were not involved in organized soccer but were allowed to participate in any other sport or activity. A total of 94 of the 195 soccer players, or 48%,
reported at least one symptom consistent with a concussion. The most prevalent symptom for these girls was headache (84%). A total of 34 of the 147 non-soccer players, or 23%, reported at least
one symptom consistent with a concussion in the previous six months. These results determined that the relative risk of probable concussions among 11- to 13-year-old, female soccer players is
2.09 (p < .001, α = .05, CI = 95%). This demonstrates that the relative risk of probable concussions in young female soccer players is significantly higher than
in a control group of non soccer players of the same sex and age.

#7 Indicators for high physical strain and overload in elite football playersAuthors: Meister S, Faude O, Ammann T, Schnittker R, Meyer T.Reference: Scand J Med Sci Sports.Summary: Laboratory, psychological and performance parameters as possible indicators of physical strain and overload during highly demanding competition phases were evaluated in
elite male football players. In two studies with the same objective, periods of high (HE: >270 min during 3 weeks before testing) and low (LE: <270 min) match exposure were compared over
the course of an entire season. In study 1 (n=88 players of the first and second German leagues; age: 25.6 ± 4.3 years; body mass index (BMI): 23.2 ± 1.0 kg/m(2) ), blood count, CK, urea, uric
acid, CRP and ferritin were determined. In study 2, 19 players of the third German league and the highest under-19 league (age: 19.7 ± 2.8 years; BMI: 22.8 ± 1.7 kg/m(2) ) were screened for
individual vertical jump height, maximal velocity and by the Recovery-Stress-Questionnaire for Athletes (REST-Q Sport). The mean differences in exposure times were 180 min (study 1: quartiles:
105, 270 min) and 247 min (study 2: 180, 347 min), respectively. Significant differences were found neither in blood parameters (study 1; P>0.36) nor in physiological testing results or in
REST-Q scores (study 2; P>0.20). A 3-week period of high match exposure in elite football players does not affect laboratory, psychometric and performance parameters.

#8 Effects of a 10-week resistance exercise program on soccer kick biomechanics and muscle strengthAuthors: Manolopoulos E, Katis A, Manolopoulos K, Kalapotharakos V, Kellis E.Reference: J Strength Cond Res. 2013 Dec;27(12):3391-401. doi: 10.1519/JSC.0b013e3182915f21.Summary: Manolopoulos, E, Katis, A, Manolopoulos, K, Kalapotharakos, V, and Kellis, E. Effects of a 10-week resistance exercise program on soccer kick biomechanics and muscle
strength. J Strength Cond Res 27(12): 3391-3401, 2013-The purpose of the study was to examine the effects of a resistance exercise program on soccer kick biomechanics. Twenty male amateur soccer
players were divided in the experimental group (EG) and the control group (CG), each consisting of 10 players. The EG followed a 10-week resistance exercise program mainly for the lower limb
muscles. Maximal instep kick kinematics, electromyography, and ground reaction forces (GRFs) as well as maximum isometric leg strength were recorded before and after training. A 2-way analysis of
variance showed significantly higher ball speed values only for the EG (26.14 ± 1.17 m·s vs. 27.59 ± 1.49 m·s before and after training, respectively), whereas no significant differences were
observed for the CG. The EG showed a decline in joint angular velocities and an increase in biceps femoris electromyography of the swinging leg during the backswing phase followed by a
significant increase in segmental and joint velocities and muscle activation of the same leg during the forward swing phase (p < 0.05). The EG also showed significantly higher vertical GRFs
and rectus femoris and gastrocnemius activation of the support leg (p < 0.05). Similarly, maximum and explosive isometric force significantly increased after training only for the EG (p <
0.05). These results suggest that increases in soccer kicking performance after a 10-week resistance training program were accompanied by increases in maximum strength and an altered soccer kick
movement pattern, characterized by a more explosive backward-forward swinging movement and higher muscle activation during the final kicking phase.